Although chemically produced drugs have a long record of success as therapeutic agents, they are not without serious limitations. The vast majority are small hydrophobic molecules that are limited in use due to their poor pharmacokinetic and pharmacodynamic properties. While much attention has focused on generating new compounds or modifying existing ones for improved efficacy, a new paradigm has emerged within the existing dogma of drug therapy. The development of nanoparticle based platforms enhances the delivery of current compounds and circumvents the adverse pharmacological properties of conventional drugs. These new drug delivery systems (DDS) overcome current limitations by offering environments for improved solubility, thereby eliminating the need for toxic organic solvents. Common examples include the use of dendrimers, liposomes, or conjugation to polymers, such as polyethylene glycol (PEG). Although the latter two have had success and have been approved for clinical use, they are not without pitfalls, such as size limitations and lack of tissue targeting. Therefore, new nanoparticles and new strategies for drug delivery are needed.
Vaults are cytoplasmic ubiquitous ribonucleoprotein particles first described in 1986 that are found in most eukaryotic cells (Kedersha et al., J Cell Biol, 103(3):699-709 (1986)). Native vaults are 12.9±1 MDa ovoid spheres with overall dimensions of approximately 40 nm in width and 70 nm in length (Kong et al., Structure, 7(4):371-379 (1999); Kedersha et al., J Cell Biol, 112(2):225-235 (1991)), present in nearly all eukaryotic organisms with between 104 and 107 particles per cell (Suprenant, Biochemistry, 41(49):14447-14454 (2002)). Despite their cellular abundance, vault function remains elusive, although they have been linked to many cellular processes, including the innate immune response, multidrug resistance in cancer cells, multifaceted signaling pathways, and intracellular transport (Berger et al., Cell Mol Life Sci, 66(1):43-61 (2009)).
Vaults are highly stable structures in vitro, and a number of studies indicate that the particles are non-immunogenic (Champion et al., PLoS One, 4(4):e5409 (2009)). Vaults can be engineered and expressed using a baculovirus expression system and heterologous proteins can be encapsulated inside of these recombinant particles using a protein-targeting domain termed INT for vault INTeraction domain. Several heterologous proteins have been fused to the INT domain (e.g., fluorescent and enzymatic proteins) and these fusion proteins can be added to the recombinant vaults and, due to the dynamic nature of the vaults, the fused INT proteins access the interior of the particle where they bind non-covalently and retain their native characteristics, thus conferring new properties onto these vaults (Stephen et al., J Biol Chem, 276(26):23217-23220 (2001); Kickhoefer et al., Proc Natl Acad Sci USA, 102(12):4348-4352 (2005)).
Vaults have also been engineered to contain a discoidal phospholipid bilayer nanodisks (NDI), by the self-assembly of a small discoidal lipid bilayer lipoprotein complex, which absorbed ATRA (Buehler, D. C., et al., Small, 2011, 7(10): 1432-9). As these nanodisks of Δapo-AI protein were conjugated with the INT domain, ATRA did not directly interact with the vault but was rather carried into the vault indirectly via this nanodisk conjugation with INT. The formation of NDI lipoprotein complexes followed by vault packaging remains a time consuming and complicated multi-step process. Furthermore, as Δapo-AI is expressed in E. coli, there is the possibility that during purification it may bind liberated host bacterial membrane constituents such as Lipopolysaccharide (LPS), an endotoxin which elicits a strong pro-inflammatory immune response and poses a risk if administered to humans (Erridge, et al., Microbes and infection/Institut Pasteur, 2002, 4(8): 837-51). Apo-AI naturally binds LPS in order to mitigate host inflammatory response thru rapid clearance via the liver (Henning, et al., Innate immunity, 2011, 17(3): p. 327-37). As such, NDI produced in bacteria may act to carry LPS to the targeted cells, possibly inducing a harmful pro-inflammatory response.
Vaults are generally described in U.S. Pat. No. 7,482,319, filed on Mar. 10, 2004; U.S. Pat. No. 6,156,879, filed on Jun. 3, 1998; U.S. Pat. No. 6,555,347, filed on Jun. 28, 2000; U.S. Pat. No. 6,110,740, filed on Mar. 26, 1999; and PCT Publication No. WO 1999/62547 filed on Jun. 3, 1998. Vault compositions for immunization against chlamydia genital infection are described in U.S. Pat. No. 8,124,109, filed on May 15, 2009. The entire contents of these applications are incorporated herein by reference in their entirety for all purposes.